1. Field of the Invention
The instant disclosure relates to a headphone with active noise cancelling; in particular, to an auto-calibration method for the headphone with active noise cancelling.
2. Description of Related Art
Nowadays, electric products are increasingly popular, and audio equipment has been important equipment that people enjoy entertainment and acquire new information, wherein the headphone is further served as an electronic device listening anywhere, anytime. In order to provide a better listening experience, it must take noise cancelling method for the headphone of the user receiving environment noise simultaneously. There are two headphones according to difference of the noise cancelling method, e.g. a passive noise cancelling headphone and an active noise cancelling headphone.
Because the passive noise cancelling headphone is merely reduce noise via audio-Insulating materials, ability for noise cancelling is extremely associated with material, thickness, structural design, conformability, so that the headphone is generally very large and heavy. Additionally, because materials used for the passive noise cancelling headphone does not isolation effect for noise in low frequency band, noise in low frequency band (e.g. an engine and a blower) does not isolated. On the contrary, there is no limit above-mentioned for the active noise cancelling headphone, so the active noise cancelling headphone is very popular for the user.
Two microphone sensors are respectively placed on front of the left speaker and right speaker of the active noise cancelling headphone commercially available usually. Moreover, in the prior art, calibration of the active noise cancelling headphone is by means of adjusting variable resistor manually, and calibration method in recent days is to adjust gain value of the microphone via a digital interface and relevant calibration result is burned in the OTP memory. However, calibration procedure is still realized by means of manual adjustment; which means, after adjusting the gain value of the headphone, the gain value is burned in the OTP memory and then performing test. Therefore, a calibration time for the headphone is very long.